Petroleum resources have constantly deteriorated and crude oil becomes more and more heavy in compositions, requirements for environmental protection are getting more and more strict, and new environmental regulations around the world have imposed more stringent requirements on gasoline quality. For instance, the National V Standard for motor gasoline which will be implemented by Jan. 1, 2017 will require olefins content to be below 24%, sulfur content to be below 10 ppm, and octane number to be above 93. Upgrading gasoline quality standard are mainly embodied in: reducing the olefins content and the sulfur content while increasing the octane number.
Currently, developed countries mainly target at improving “formulations” of the gasoline to meet a corresponding quality standard. They use various processes to manufacture gasoline, and then blend various types of gasoline. Generally, in the gasoline, fluid catalytic cracking gasoline containing olefins accounts for about less than ⅓, reformulated gasoline which contains aromatics but frees of olefins accounts for about more than ⅓, and other clean gasoline components subjected to alkylation, isomerization and etherification which contains neither aromatics nor olefins account for about ⅓. The sulfur content and the olefins content are low, and the octane number is high.
The fluid catalytic cracking gasoline is a major part of China's motor gasoline, which accounts for about 75% in a gasoline pool. Approximately 90% of olefins content and sulfur content in finished gasoline comes from the fluid catalytic cracking gasoline, resulting in that China's gasoline products are far from meeting new index requirements of sulfur content ≤10 ppm and olefins content ≤24%. In another aspect, currently, mainly 93# gasoline is used China, however, as the manufacturing technology of domestic automotive industry continuously improves and domestic retention quantity of imported automobile unceasingly increases, there is an increasing demand for 95# gasoline or gasoline with higher octane number. Since the fluid catalytic cracking gasoline is limited by the process itself, octane number thereof is maintained primarily by large amounts of olefins, and RON is generally about 90, thus the octane number of the fluid catalytic cracking gasoline directly influences the octane level of the finished gasoline. Moreover, at present, a main process for removing sulfur and lowering olefins in fluid catalytic cracking gasoline is catalytic hydrogenation, which inevitably leading to large amounts of olefins being saturated, resulting in a greater loss of octane number, and seriously affecting economic returns of enterprises.
As crude oil becomes increasingly heavier in compositions, the catalytic cracking capacity of heavy oil is expanded constantly and environmental regulations become increasingly stringent, this problem mentioned above is more prominent, which is objectively forcing the petrochemical industry to research and develop new processes for upgrading the fluid catalytic cracking gasoline efficiently, especially an efficient upgrading process which can realize both deep desulfurization of the fluid catalytic cracking gasoline and improvement of the octane number.
Existing sulfur reduction techniques of the fluid catalytic cracking gasoline are mainly represented by S-zorb of Sinopec, RSDS of Sinopec Research Institute of Petroleum Processing and Prime-G+ of French. S-zorb is developed by U.S. Conocophillips Corporation, bought out and improved by Sinopec Group, and is used for desulfurization of full-range fluid catalytic cracking gasoline, the sulfur content of the full-range gasoline after desulfurization may be controlled to be below 10 ppm, and an octane number loss of the full-range gasoline is 1.0˜2.0 units. RSDS is developed by Sinopec Research Institute of Petroleum Processing, this technique firstly cuts catalytic gasoline into light and heavy gasoline fractions, then the light gasoline fraction is subjected to sweetening by extraction, and the heavy gasoline fraction is subjected to selective hydrodesulfurization; when a product with sulfur content of less than 10 ppm is manufactured by this technique, the yield of light gasoline fraction is about 20%, most of the fractions requires hydrogenation, and an octane number loss of the full-range gasoline is between 3.0˜40. Prime-G+ is developed by French Axens Corporation, which uses a technological process comprising full-range prehydrogenation, cutting of light and heavy gasoline and selective hydrodesulfurization of heavy gasoline fraction, and is characterized by reaction light sulfide with diolefins to form a sulfide with high boiling point during the full-range prehydrogenation process, where olefins is not saturated, and then light gasoline fraction with sulfur content less than 10 ppm and heavy gasoline fraction with high sulfur content are obtained by cutting of light and heavy gasoline, and the heavy gasoline fraction is subjected to hydrodesulfurization; this technique is the same as RSDS, although a part of light gasoline fraction with low sulfur content may not be subjected to hydrogenation, since light gasoline fraction with sulfur content less than 10 ppm have a low yield, most of the fractions requires hydrogenation, resulting in that the octane number loss of the full-range gasoline is also between 3.0˜4.0.
CN1611572A discloses a catalytic conversion method for improving octane number of gasoline. This method enables heavy gasoline fraction having an initial boiling point greater than 100° C. to be contacted with a catalyst having a temperature lower than 700° C., and reacted in a condition where a temperature is 300˜660° C., a pressure is 130˜450 KPa, a weight hourly space velocity is 1˜120 h−1, a weight ratio of the catalyst to the gasoline fractions is 2˜20, and a weight ratio of steam to the gasoline fractions is 0˜0.1, and a reaction product is separated from a coked catalyst, where the coked catalyst is recycled by stripping and regeneration. Octane number of fluid catalytic cracking gasoline may be increased by 3˜10 units by using the method provided in the present invention. This method follows a catalytic cracking mechanism of oil hydrocarbons, subjecting gasoline to a hydrogen transfer reaction and a cracking reaction, although octane number of the gasoline can be improved, the cutting of fractions need to be carried out firstly, and only the heavy gasoline fraction having the initial boiling point greater than 100° C. are collected for the reaction, thus there is a great loss of gasoline.
CN1160746A discloses a catalytic conversion method for improving octane number of low-grade gasoline. This method enables gasoline having low octane number to be contacted with a high temperature catalyst coming from a regenerator by injecting the gasoline into a riser reactor from an upstream of an inlet of a conventional catalytic cracking feedstock, and reacted in a condition where a reaction temperature is 600˜730° C., a ratio of the catalyst to the gasoline is 6˜180, and a weight hourly space velocity is 1˜180 h−1. This method may increase octane number of the gasoline, but all the gasoline having low octane number in the method is required to participate in the reaction, thus there is a great loss of gasoline.
CN103805269A proposes a method for deep hydrodesulfurization of catalytic gasoline, a clean gasoline product is obtained by subjecting light gasoline and medium gasoline fractions to alkali-free sweetening, then separating the light and the medium gasoline through a hydrogenation pre-fractionating tower, where the hydrogenation pre-fractionating tower is imported with hot diesel simultaneously; subjecting the separated medium gasoline and heavy gasoline to selective hydrogenation after blending them, and blending the resulted distillate oil with the light gasoline being subjected to alkali-free sweetening. Although this method can realize effective desulfurization and a degree of decrease of octane number is also alleviated to some extent, the octane number cannot be increased effectively, and there are considerable differences between the technological process of this method and that of the present invention.
In conclusion, generally, there are problems such as a large proportion of hydrogenation and a great loss of octane number when a current technique dealing with the deep desulfurization requirement of fluid catalytic cracking gasoline. Effects of some supporting processes for restoring octane number during hydrodesulfurization are not obvious either. There is a pressing demand on the market to develop a technique for deep desulfurization of fluid catalytic cracking gasoline, which has less loss of octane number or significant rise of octane number.